Removal of sulfur contaminants from hydrocarbon streams



United States Patent C Theodore J. Peters, Somerville, and Albert Gathman,

Neptune, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application September 11, 1957 Serial No. 683,217

7 Claims. 01. 260- 639 "This invention relates to the preparation of a substantially isoalkene free 0.; to C normal alkene containing hydrocarbon stream having a reduced sulfur content. I na preferred embodiment, this invention relates to an improved process for the recovery of a substantially isobutylene free normal butylene bearing stream containing a reduced sulfur content from a crude hydrocarbon mixture comprising initially butanes, butylenes, mercapt'ans and other sulfur contaminants and usually small amounts of C and C hydrocarbons. This inven- .tion further relates to the separation of a n-butylene containing stream of low sulfur content from a hydrocarbon stream containing normal and isobutylenes having a higher sulfur content. The term sulfur content or contaminant as employed herein is meant to include sulfur in its elemental form and/or in the form of its various organic and inorganic compounds. This invention further relates to the use of these isoalkene free normal alkene streams containing low sulfur content in the preparation of alcohols having the same number of carbon atoms as the alkene, such as secondary butyl alcohol from n-butylene.

There are two processes for the preparation of alcohols from olefins which are in successful commercial operationytoday. Broadly speaking, the first process comprises the acid extraction technique wherein the hydrocarbon stream containing olefin is contacted with an aqueous mineral acid such as sulfuric or phosphoric to form an acid extract. This acid extract may then be hydrolyzed with steam and/or Water to form the desired alcohol product which may subsequently be finished to ahigh degree of purity. The second major process suitable for commercial use comprises what is known as the direct hydration technique. In the direct hydration technique the olefins such as butylenes are contacted under isevere reaction conditions with water in the presence of *a synthetic acid resin catalyst such as an ion exchange resin possessing essentially a hydrocarbon skeleton combined with a strong mineral acid group, eg sulfonic radical.

The removal of sulfur from the olefin feed and/or alcohol product to a point where the alcohol product is acceptable to the trade is a serious problem confronting the manufacturers of these alcohols. The olefin containinghydrocarbon streams employed in the preparation of alcohols is unavoidably contaminated with sulfur contaminants which may be present in various forms. it is accordingly necessary to remove sulfur from the olefin bearing stream as completely as possible without making the process economically unattractive. In general, the

*prior art has scrubbed the olefin bearing stream with sulfur removing agents such as aqueous caustic soda or other alkaline agents. While this treatment effects a substantial reduction in sulfur contaminants, there never- -theless appear to be sulfur contaminants which either cannot be or are'ditficult to remove by commercial distillation and/or scrubbing techniques. Accordingly, the

alcohol derived from these olefins are contaminated with considerable sulfur, e.g. 20-50 parts per million and require extensive finishing steps to produce a commercially acceptable product. To illustrate the above noted alco hol preparation techniques, a brief description of both types will follow. For the sake of convenience both the direct hydration and acid extraction techniques will be described with reference to the production of secondary butyl alcohol although it is to be: understood that this process is amenable to the preparation of the C to C alkenes and the corresponding alcohols.

The acid extraction technique employs cracked gases from petroleum oil refinery streams as a source of the normal butylene to form the acid extract which is subsequently hydrolyzed and distilled to recover the alcohol. These cracked gases may be produced by thermal, catalytic or steam cracking of hydrocarbon oils and are generally a heterogeneous mixture of saturated hydrocarbons, e.g. butanes; normal olefins, e.g. butylenes; tertiary olefins, e.g. isobutylene and smaller quantities of diolefins. Thus a typical mixed C olefin stream will cornprise butane 49.4%, n-butylenes 34.2%, isobutylene 14.3%, sulfur contaminants -200 p.p.m. and small amounts of mixed C and C hydrocarbons 2.1%. It is to be understood, of course, that the composition of the C feed may vary considerably depending on the particular source and it is only necessary for the purposes of this invention that the feed contain substantial amounts of normal butylenes and isobutylenes. The entire process for the preparation of secondary butyl alcohol via this general acid hydrolysis route comprises feeding a mixed C olefin stream such as described above first through an aqueous caustic scrubber to remove a substantial amount of the objectionable sulfur contaminants such as mercaptans and the like. Preferably, the olefin feed is in a mixed liquid and gaseous phase. The caustic scrubbed hydrocarbon feed is then passed through an isobutylene extraction unit wherein the feed is treated with an aqueous sulfuric acid solution of medium strength. With specific sulfuric acid concentrations the isobutylene is selectively extracted from the olefin mixture. The aqueous acid extract of isobutylene is removed as a separate phase and may be hydrolyzed to recover isobutylene for its well-known uses which are not pertinent to this invention. The remaining portion of the feed comprising principally butanes and normal butylenes is then passed through a normal butylene extraction zone wherein the hydrocarbon stream is contacted with a stronger sulfuric acid solution which selectively extracts the n-butylenes. The aqueous acid extract containing n-butylene is then passed to a hydrolysis zone wherein steam and water are employed to hydrolyze the extract forming crude secondary butyl alcohol. The crude alcohol may then be treated by various known finishing techniques to recover a relatively pure alcohol if desired.

in ilifi direct hydration technique the normal butylene containing feed which remains after isobutylene is re moved as above described or by other means is passed with water generally in liquid phase, although a liquidgaseous phase may be employed, through a closed conversion zone under elevated temperatures and usually ele vated pressures in contact with a sulfonated synthetic ion exchange resin in its acid form. One such typical resin is known as Dowex SOXS made by the Dow Chemical Co. which corn rises a sulfonated resinous copolymer of about 92% styrene and 8% divinyl benzene and contains about 44 to 50% moisture and about 12 to 16% sulfur in the sulfonate form, based on anhydrous resin. It is to be understood that the specific resin composition employed in the direct hydration technique is one of choiceand may be selected from numerous resins now on the market. The crux of this invention relates .to the; production of :a

substantially isobutylene free normal butene containing stream having a reduced sulfur content. However, since this butene stream may be employed for the production of alcohols either via the direct hydration route or the acid extractionprocess, a full description for the production of alcohols via one of the processes will be given for the purpose of amplifying the disclosure.

A crude refinery C olefin stream containing butane 40 to 60%, isobutylene 7 to 20%, small amounts of C and C hydrocarbons, and n-butylenes 20 to 42% is contacted with aqueous caustic soda of from 12 to 17 B. or other known sulfur removing alkaline agents in a scrubbing zone which may be of conventional design. Although not required, elevated temperatures and pressures may be employed in this stage. The caustic treated olefin feed is then contacted with sulfuric acid of preferably of 60 to 70 wt. percent in a volume ratio generally from 5 to 20 volumes of liquid hydrocarbon per volume of sulfuric acid. Conditions Within the extraction zone must be maintained between 50 to 120 F. and preferably from 70-100 F. and with pressures from 15 to 125 p.s.i.g.and preferably from 100-110 p.s.i.g. These conditions are not only necessary for the efficient and selective extraction of isobutylenes, but have been found to be necessary for the efficient conversion of sulfur contaminants remaining in the hydrocarbon stream to higher boiling products. It has been found that when employing these conditions a substantial amount of the remaining sulfur can be converted to thioethers which boil outside the C -C hydrocarbon range. The remaining hydrocarbon stream substantially free of isobutylene is then passed through a distillation zone whereby high bo ling contaminants are removed as bottoms. The conditions for distillation which effect a substantially complete removal of sulfur contaminants from the substantially isobutylenefree hydrocarbon stream are pressures of to 10 p.s.i.g., e.g. 0 p.s.i.g., an overhead temperature of 32- 203 F., and a bottoms temperature of 203-320 F. At this point the isobutylene free (i.e. about 1%) feed may be employed in the well-known direct hydration tech- =niqueas generally noted above or in the acid extract bydrolysis which will be defined in more detail below. The distillate now substantially reduced in sulfur content and being substantially free from sulfur contamination is then passed through a conventional normal butylene extraction zone wherein the hydrocarbon stream is contacted --with sulfuric acid having a concentration of from 70-80 -wt. percent, whereby n-butylenes are selectively extracted. ;In the nbutylene extraction zone a substantially greater ratio of acid to hydrocarbon feed is employed to effect a greater recovery of n-butylenes present. For example, a

ratio of from 1-10 liquid volumes of hydrocarbon per volume of sulfuric acid is employed. Reaction conditions for the n-butylene extraction may comprisea temperature of 80 to 135 F. and preferably 105-115 F. and a pressure of to 125 p.s.i.g., preferably 85-95 p.s.i.g. The aqueous normal butylene acid extract is then passed to a final hydrolysis stage wherein the extract is contacted with water and/or steam under atmospheric -orelevated pressures, e.g. up to 100 p.s.i.g., and elevated temperatures of from ZOO-300 F. stage polymers, olefins and ethers formed as a result of In the hydrolysis the dilution of the concentrated sulfuric acid are removed overhead and crude secondary butyl alcohol which is substantially sulfur-free is recovered as a side stream.

It has been discovered that sulfur contaminants which cannot be removed by normal sulfur removal techniques such as scrubbing and pro-distillation procedures are converted into higher boiling sulfur compounds during the instant isobutylene extraction stage and that the n-butylone containing stream can be distilled from the higher boiling sulfur contaminants to effect a normal butylene containing stream substantially free of sulfur compounds. The sulfur content, however, is concentrated as the proc- 'ess progresses since substantially no sulfur is removed with the isobutylene acid extract and a disproportionately 4 a a small amount of sulfur is carried off with the butanes. The increase in sulfur content on a weight percent basis with regard to the final n-but ylene extract will depend on the proportionate amounts of the butanes, isobutylenes and n-butylenes present in the crude feed.

Distillation of the feed prior to isobutylene extraction does not effect an appreciable removal of sulfur since prior to the extraction the remaining sulfur contaminants boil in the range of the C stream.

Examples 2 and 3 show the marked improvement obtained by resort to distillation subsequent to the isobutylene extraction as contrasted with the process of Example 1 wherein no post-distillation step is employed.

Example 1 A mixed C olefin feed having the composition described previously was scrubbed with aqueous caustic of 15 Be. under atmospheric conditions.- The caustic scrubbed feed was then contacted with 65-66% sulfuric acid at a temperature of about F. and a pressure of p.s.i.g., employing about 9 volumes of hydrocarbon per volume of sulfuric acid. The hydrocarbon phase containing n-butylenes and being substantially free of isobutylene was analyzed and found to contain 20 parts per million of sulfur. The normal butylene was then extracted from the hydrocarbon phase at F., a pressure of 90 p.s.i.g. with 76-77 wt. percent sulfuric acid using a hydrocarbon to acid ratio of about 2V2 to 1 The acid extract was then hydrolyzed with steam and water at 19 p.s.i.g. and 255 F. to produce secondary butyl alcohol. A crude alcohol of 72% purity was recovered by distillation.

Example 2 Example 3 In a subsequent test employing the same conditions as in Example 2 and using a feed containing a smaller amount of sulfur, the sulfur contamination was reduced from 17.4 parts per million to 5.2 parts pervmillion. Bottoms contained 2100 p.p.m.sulfur. M I

What is claimed is:

1. A process for the preparation of asubstantially isoallcene free C to C normal alkene containing hydrocarbon stream having a reduced sulfur content which comprises extracting isoalkene from a sulfur contaminated hydrocarbon stream containing C -C alkenes and isoalkene with 60-70 wt. percent sulfuric acid at 50 to F. and a pressure of 15 to p.s.i.g., utilizing a hydrocarbon to acid ratio of from 5 to 20 parts. of hydrocarbon to 1 part of acid, whereby said sulfur contaminants are converted to higher boiling compounds, recovering a normal alkene comprising stream being substantially free of isoalkene and contaminated with higher boiling sulfur contaminants and distilling said stream to recover a normal alkene comprising stream being substantially free of sulfur contaminants.

2. A process in accordance with claim 1 wherein said sulfur contaminated hydrocarbon stream containing C to C alkenes and isoalkenes is first scrubbed by an butylene free containing hydrocarbon, stream hav ing..a

reduced sulfur content which comprises extracting isobutylene from a sulfur contaminated hydrocarbon stream containing isobutylene and normal butylenes with 60-70 wt. percent sulfuric acid at 70 to 100 F. and a pressure of 100 to 110 p.s.i.g., utilizing a hydrocarbon to acid ratio of from 5 to 20 parts of hydrocarbon to 1 part of acid, whereby said sulfur contaminants are converted to higher boiling compounds, recovering a normal butylene comprising stream being substantially free of isobutylene and contaminated with higher boiling sulfur contaminants, and distilling said stream to recover a normal butylene comprising stream being substantially free of sulfur contaminants.

5. A method in accordance with claim 4 wherein said sulfur contaminated hydrocarbon stream is first scrubbed with an alkaline scrubbing agent to reduce the sulfur contaminant therein.

6. A method in accordance with claim 5 wherein said alkaline agent is aqueous caustic soda.

7. In a process for the preparation of secondary butyl alcohol wherein a normal butylene containing hydrocarbon stream containing also isobutylenes and sulfur contaminants is scrubbed with an alkaline agent to reduce the sulfur contaminants thereof and wherein the scrubbed normal butylene containing stream is substantially freed of isobutylene by extraction with -70 wt. percent sulfuric acid and wherein the resultant isobutylene free normal butylene stream is contacted with sulfuric acid to extract the normal butylenes which are subsequently hydrolyzed to form a crude secondary butyl alcohol product, the improvement which comprises extracting the isobutylene from said butylene stream with 60-70 wt. percent sulfuric acid at to 110 F. and a pressure of to p.s.i.g., utilizing a hydrocarbon to acid ratio of from 5 to 20 parts of hydrocarbon to 1 part of acid, whereby sulfur contaminants within said normal butylene containing stream are converted to higher boiling sulfur contaminants and distilling the substantially isobutylene free normal butylene stream to recover a distillate having a reduced sulfur content.

References Cited in the file of this patent UNITED STATES PATENTS 2,394,678 Frankel et al Feb. 12, 1946 2,514,291 Patterson July 4, 1950 2,826,615 Campbell Mar. 11, 1958 

1. A PROCESS FOR THE PREPARATION OF A SUBSTANTIALLY ISOALKENE FREE C4 TO C6 NORMAL ALKENE CONTAINING HYDROCARBON STREAM HAVING A REDUCED SULFUR CONTENT WHICH COMPRISES EXTRACTING ISOLAKENE FROM A SULFUR CONTAMINATED HYDROCARBON STREAM CONTAINING C4-C6 ALKENES AND ISOALKENE WITH 60-70 WT. PERCENT SULFURIC ACID AT 50 TO 120* F. AND A PRESSURE OF 15 TO 125 P.S.I.G., UTILIZING A HYDROCARBON TO ACID RATIO OF FROM 5 TO 20 PARTS OF HYDROCARBON TO 1 PART OF ACID, WHEREBY SAID SULFUR CONTAMINANTS ARE CONVERTED TO HIGHER BOILING COMPOUNDS, RECOVERING A NORMAL ALKENE COMPRISING STREAM BEING SUBSTANTIALLY FREE OF ISOALKENE AND CONTAMINATED WTH HIGHER BOILING SULFUR CONTAMINANTS AND DISTILLING SAID STREAM TO RECOVER A NORMAL ALKENE COMPRISING STREAM BEING SUBSTANTIALLY FREE OF SULFUR CONTAMINANTS.
 7. IN A PROCESS FOR THE PREPARATION OF SECONDARY BUTYL ALCOHOL WHEREIN A NORMAL BUTYLENE CONTAINING HYDROGEN BON STREAM CONTAINING ALSO ISOBUTYLENES AN SULFUR CONTAMINANTS IS SCRUBBED WITH AN ALKALINE AGENT TO REDUCE THE SULFUR CONAMINATNTS THEREOF AND WHEREIN THE SCRUBBED NORMAL BUTYLENE CONTAINING STREAM IS SUBSTANTIALLY FREED OF ISOBUTYLENE BY EXTRACTION WITH 60-70 WT. PERCENT SULFURIC ACID AND WHEREIN THE RESULTANT ISOBUTYLENE FREE NORMAL BUTYLENE STREAM IS CONTACTED WITH SULFURIC ACID TO EXTRACT THE NORMAL BUTYLENES WHICH ARE SUBSEQUENTLY HYDROYLZED TO FORM A CRUDE SECONDARY BUTYL ALCOHOL PRODUCT, THE IMPROVEMENT WHICH COMPRISES EXTRACTING THE ISOBUTYLENE FROM SAID BUTYLENEN STREAM WITH 60-70 WT. PERCENT SULFURIC ACID AT 70 TO 110*F. AND A PRESSURE OF 100 TO 110 P.S.I.G., UTILIZING A HYDROCARBON TO ACID RATIO OF FROM 5 TO 20 PARTS OF HYDROCARBON TO 1 PART OF ACID, WHEREBY SULFUR CONTAMINANTS WITHIN SAID NORMAL BUTYLENE CONTAINING STREAM ARE CONVERTED TO HIGHER BOILING SULFUR CONTAMINATNTS AND DISTILLING THE SUBSTANTIALLY ISOBUTYLENE FREE NORMAL BUTYLENE STREAM TO RECOVER A DISTILLATE HAVING A REDUCED SULFUR CONTENT. 